As the electronics industry advances and production of light weight components increases, the development of new materials gives producers increased options for further improving the performance and ease of manufacture of such components. Adhesive compositions are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses include bonding of electronic elements such as integrated circuit chips to lead frames or other substrates, and bonding of surface mount components to printed circuit boards.
Adhesives useful for electronic packaging applications typically exhibit properties such as good mechanical strength, curing properties that do not affect the component or the carrier, and rheological properties compatible with application to microelectronic and semiconductor components. Examples of such packages are ball grid array (BGA) assemblies, super ball grid arrays, IC memory cards, chip carriers, hybrid circuits, chip-on-board, multi-chip modules, pin grid arrays, and the like.
Commercially available adhesives for low temperature cure applications are generally two part epoxy/polythiol compositions. Two part systems are cumbersome to work with due to the short pot-life once the two components are mixed together. Furthermore, in situ mixing of the two components can be inconsistent and unreliable, and is not practical for large-scale manufacturing application. The demand for one-part systems with adequate room temperature stability for several hours to 1 day or more is very high.
Currently available one-part adhesive systems contain an epoxy, a polythiol, and a latent curing accelerator. These systems necessarily employ glycidyl ether and/or glycidyl ester epoxies as these are the only epoxies that are sufficiently reactive with thiol curatives to be practical as adhesives. Both glycidyl ethers and esters are known for their residual chlorine content. Even the “cleanest” versions of these monomers contain around 50 ppm of total chloride. However, chloride ions are a potent source of corrosion in electronic components and thus, many applications of adhesive compositions are intolerant of chloride. Thus, one-part adhesive systems have limited usefulness in many of the most important electronics applications.
The microelectronics industry continues to require new resins that are able to meet its varying demands. There is thus a need for the development of new materials to address the requirements of this rapidly evolving industry.